The present invention generally relates to ram air turbines of the type used on aircraft to drive backup electric or hydraulic power systems and, more particularly, to a ram air turbine having an in-line speed increasing planetary gearbox for driving an electrical generator or hydraulic pump.
Ram air turbine power systems (RATs) are generally known in the aerospace industry for use in driving auxiliary power systems in the event of a primary system failure. Commercial aircraft manufacturers install RATs as an emergency form of power when the main engine generators or hydraulic pumps are not operating. The ram air turbine power system is commonly stored within the wing or fuselage of an aircraft for deployment into the air stream when needed. When called upon for electrical power, the RAT is deployed into the air stream, typically by swinging it out from its wing or fuselage compartment at the end of a support strut, and functions similar to a windmill by extracting energy from the flowing air along the aircraft in flight. The ram air turbine portion of the RAT typically includes two or more turbine blades adapted to be driven by the air stream, to provide a rotary output which can be used to drive an electrical generator, a hydraulic pump or both. Such ram air turbines are commonly equipped with a speed control governor for altering turbine blade pitch angle, or feathering, to achieve a substantially constant turbine rotational speed despite variations in air speed or load.
When designing aircraft components, important factors to address are size, weight, and reliability. In an effort to reduce the physical size, also referred to as “envelope”, of an electrical generator or other power source device that is driven by a RAT, one method is to increase the speed at which the generator or other power source device operates. But the RAT turbine may have an optimum speed that is slower than the increased generator speed. Prior art, for example, U.S. Pat. No. 5,484,120, teaches the use of a gear train as a means of transmitting shaft rotation up through a hollow support strut between the RAT turbine and a driven device at the top of the support strut within the aircraft, using spur gears and bevel gears. The use of such a drive shaft extending through the support strut to drive a power source device within the aircraft is comparatively long and heavy relative to using a short drive shaft to drive the power source device adjacent to the RAT turbine, and the spur gears and bevel gears may sustain a relatively high gear tooth loading, detracting from reliability. The problem of reducing generator envelope and weight is not addressed.
As can be seen, there is a need to reduce the envelope and weight of RATs while improving their reliability. There is also a need for reducing the envelope and weight of the generator or other power source device driven by the RAT turbine. Moreover, there is a need for providing an efficient arrangement of components in the RAT.